1. Field of the Invention
This invention relates to novel catalysts for the catalytic destruction of organic compounds contained in waste gas streams and to a process using these catalysts.
2. Description of Related Art
Presently, there is great concern about contamination of the environment by hazardous volatile organics originating in the manufacture of organic chemicals, cleaning and degreasing processes, and vent or exhaust air from air stripping of contaminated groundwater or soil. Typically, thermal incineration is used in the destruction of these materials but this requires very high temperatures (1300.degree. C.) and special equipment resulting in high capital and maintenance costs. Carbon adsorption is an alternative. However, this process does not destroy the pollutants but merely concentrates them. The pollutants must then be removed and the carbon regenerated, a costly and tedious process.
Catalytic oxidation is an energy efficient and economical way of destroying hazardous materials. It operates at significantly lower temperatures and lower residence times than thermal incineration and requires smaller reactors made of less expensive materials.
Methods for the catalytic oxidation of organic and halogenated organic compounds are well known in the art. For example, in the article by G.C. Bond and N. Sadeghi, "Catalyzed Destruction of Chlorinated Hydrocarbons" J. Appl. Chem. Biotechnol., 1975, 25, 241-248, it is reported that chlorinated hydrocarbons are converted to HCl and CO.sub.2 over platinum on gamma alumina catalyst.
U.S. Pat. Nos. 3,972,979 and 4,053,557 describe the decomposition of halohydrocarbons by oxidation over chromium oxide or a boehmite supported platinum.
U.S. Pat. Nos. 4,059,675, 4,059,676 and 4,059,683 describe methods for decomposing halogenated organic compounds using catalysts containing ruthenium, ruthenium-platinum and platinum, respectively, in the presence of an oxidizing agent at a temperature of at least 350.degree. C.
The article by James J. Spivy, "Complete Catalytic Oxidation of Volatile Organics," Ind. Eng. Chem. Res., 1987, 26, 2165-2180, is a review of the literature dealing with the heterogenous catalytic oxidation of volatile organic compounds.
The article by S. Chatterjee and H. L. Greene, "Oxidative Catalysis of Chlorinated Hydrocarbons by Metal-Loaded Acid Catalysts," Journal of Catalysis, 130, 76-85 (1991), reports on a study of the catalytic oxidation of methylene chloride in air using supported zeolite catalysts H--Y, Cr--Y and Ce--Y.
U.S. Pat. No. 4,983,366 describes a method for the catalytic conversion of waste gases containing hydrocarbons, halogenated hydrocarbons and carbon monoxide by passing the waste gases through a first zone containing a catalyst such as aluminum oxide, silicon dioxide, aluminum silicate and/or a zeolite optionally containing oxidic compounds of barium, manganese, copper, chromium, manganese and nickel, and then through a second zone containing a catalyst such as platinum and/or palladium or platinum and rhodium.
PCT international application No. PCT/U.S. 90/02386 describes a catalytic process for converting or destroying organic compounds including organohalogen compounds using a catalyst which contains as a catalytic component titania and the preferred catalyst also contains vanadium oxide, tungsten oxide, tin oxide, and at least one noble metal selected from the group consisting of platinum, palladium and rhodium characterized in that the vanadium oxide, tungsten oxide and noble metals are uniformly dispersed on the titania.
There is still a need for catalysts and processes for the oxidative destruction of halogenated organics and other organic compounds which provide improved activity and stability.